The present invention relates to an electron microscope for the observation of point defects, impure atoms and their clusters which exist at joint interfaces and contacts in an integrated device formed into a layered structure such as a memory or fast-calculation device.
The present invention also relates to an electron detection instrument for an electron microscope, especially for the purpose described above. More particularly, it concerns an electron detection instrument for observing an electron microscope image corresponding to a specific atomic configuration or crystal structure of a specimen by way of measuring scattered, diffracted, refracted, or transmitted electrons through a specimen at a high sensitivity and a high signal-to-noise ratio in a desired range of detection angle.
As described in Proc. Mat. Res. Soc. Symp. Vol. 183 (Materials Research Society, San Francisco, 1990) p. 55, the conventional electron microscope can be used for inferring a 3-dimensional atomic arrangement from several electron microscope images observed from different directions. In addition, a technique for obtaining a 2-dimensional image of a 3-dimensional atomic structure is disclosed in Japanese Patent Laid-open No. 61-78041.
On the other hand, a prior electron detection instrument for an electron microscope is constructed as shown in FIG. 18, disclosed in the "Ultramicroscopy," 28, (1989), 240. In the figure, the electron detection instrument is placed in an STEM (scanning transmission electron microscope). The STEM comprises an electron gun 20, illumination lenses 21, electron deflector coils 22, and objective lenses 23. The electron detection instrument comprises an electron-photon converting scintillator 31, light guides 32, photomultipliers 33, and a monitor 34. There are provided two separate electron detection instruments for use of different detected electrons. One electron detection instrument is for observing a dark-field image only with electrons scattered at a high angle, having an annular scintillator 31a. The other electron detection instrument is for observing a bright-field image only with transmitted electrons at a low angle, having a circular scintillator 31b. In operation, the scintillator 31 detects electrons from the specimen, and then converts these electrons to photons. These photons are fed to the photomultiplier. A signal output of the photomultiplier 33 corresponds to intensity of the electrons. The output signal is synchronized with scanning the incident electron beam by a scanning circuit 25 before being brightness-modulated and displayed on the monitor 34. The monitor 34 shows an electron microscope image.
A prior imaging instrument for electron microscope is constructed as shown in FIG. 19, the instrument being described in the "Instruction Manual Model 622SC Fiber Optically Coupled TV System," 1991, Gatan Inc., 6678 Owens, Dr, Pleasanton, Calif. 94588. To pick up an electron microscope image, the imaging instrument is placed on a flange provided at a bottom of a camera chamber 28 of the electron microscope. The imaging instrument comprises an electron-photon converting scintillator 41, optical fiber plates 42, an image intensifier 43, a prior photoconduction-type imaging device 44, an imaging device control system 45, and a monitor 34. One optical fiber plate 42 is placed between the scintillator 41 and image intensifier 43 and the other optical fiber plate 42 between the image intensifier 43 and the photoconduction-type imaging device 44, the both being faced with each other to couple. The prior photoconduction-type imaging device 44 was a imaging tube (representative trade name: Newbicon) having Zn.sub.1-x Cd.sub.x Te used for a photoconduction face thereof or a imaging tube (representative trade name: SIT tube) having Si used for a photoconduction face thereof. The quantum effect of both imaging tubes 44 become maximum at a light wavelength of 500 to 750 nm. To make a highly sensitive imaging, the scintillator 41 used for converting an electron image to optical image was the one disclosed in, for example, "Electron Microscopy," Japanese Society of Electron Microscopy, Vol. 27, No. 2, p. 170 (1992). The scintillator 1 has a YAG (Y.sub.3-x Ge.sub.x Al.sub.5 O.sub.12) of 550 nm peak luminescence wavelength doped with cerium or GOS (Gd.sub.2 O.sub.2 S) of 510 nm peak luminescence wavelength doped with praseodymium, cerium, or fluorine.
In FIG. 19, electrons transmitted through specimen (not shown) pass through electron lenses 26, and form an electron microscope image on a fluorescent plate 27, whenever a fluorescent plate 27 closes an opening separating a column 29 and a camera chamber. In operation of the imaging apparatus, at first a fluorescent plate 27 is drawn up from the opening so as to project an electron microscope image onto the scintillator 41.
The scintillator 41 converts electrons to photons. The converted photons are in proportion to intensity of the electron microscope image, or number of the electrons per area. The photons pass the optical fiber plate 42 before coming to the image intensifier 43. The image intensifier 43 converts photons to electrons to magnify-more than 100 times before converting the electrons to photons again. The magnified photons pass the optical fiber plate 42 to the photoconductive-film of the photon reception surface of the photoconduction-type imaging device 44 to emit electron-hole pairs. The generated current is detected by an electron beam emitted from an electron gun of the photoconduction-type imaging device 44 to obtain an output signal. The electron beam is scanned at a TV rate of 1/30 sec per screen. As a result, the electron microscope image on the photoconductive film can be picked up in the same way as an ordinary TV camera.